MicroRNAs regulating meis1 expression and inducing cardiomyocyte proliferation.

Cardiovascular disease has been the biggest killer in the United States for decades, with almost a million new cases each year. Even though mammalian rodent neonatal cardiomyocytes show proliferative potential for up to 5 days, adult cardiomyocytes lose this ability. Insufficient cardiomyocyte proliferation is one of the major reasons for the lack of regeneration of myocardial tissue, post injury. Several studies have looked at the mechanisms responsible for the arrest in proliferation at an adult stage. Following up on a recent study by Eulalio et al's study on functional screening of 875 miRNAs for neonatal cardiomyocyte proliferation, we recently identified several miRNAs that induce proliferation in naturally senescent adult cardiomyocytes. Additional studies by Mahmood et al 2013 have identified Meis1 as the major regulator of cardiomyocyte cell cycle. In our present study we have identified three of the adult cardiomyocyte proliferation inducing miRNAs to have binding sites on the 3'UTR of Meis1 gene by in-silico analysis and luciferase assay. Additionally we found these miRNAs; miR-548c-3p, miR-509-3p, and miR-23b-3p to induce significant proliferation in adult cardiomyocytes through translational inhibition of Meis1. We found a significant increase in the number of ACMs with each miRNA, in combination, and with siRNA mediated inhibition of Meis1 gene. We confirmed that these microRNAs, through inhibition of Meis1, affect its downstream targets and thereby regulate cell-cycle progression. Further investigating of the mechanism of action of these miRNAs can identify other treatment options for abnormalities associated with the lack of cardiac regeneration post myocardial injury.